Spark Plasma Sintering of Tungsten Bronze Sr_(2-x)Ca_xNaNb_5O_(15) (x = 0.1) Piezoelectric Ceramics: Ⅰ, Processing and Microstructure

摘要

Tungsten bronze Sr_(2-x)Ca_xNaNb_5O_(15) (SCNN, x = 0.1) piezoelectric ceramics were prepared by a novel super-fast sintering technique, i.e., spark plasma sintering (SPS). Sintering was conducted at temperatures ranging from 1000° to 1200℃ under vacuum under 35 MPa. The heating rate varied from 30° to 300℃/min and the soaking time was in the range of 5 to 60 min. The microstructure and the phase identification were analyzed via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The density of the sintered ceramics increased with an increase in sintering temperature as well as in heating rate. Materials with a near-theoretical density could be attained by sintering at 1200℃ for 5 min with a heating rate of 300℃/min, exhibiting a homogeneous and fine-grained micro-structure (grain size about 2.7μm) and a uniform translu-cency. A tetragonal tungsten bronze phase was identified in ceramics sintered at temperatures above 1200℃, whereas the tungsten bronze phase transformed to a SrNb_2O_6-type phase in the materials sintered at temperatures below 1200℃. XRD patterns demonstrated a preferred crystallographic orientation of the SCNN grains with their c-axes perpendicular to the pressing direction.